Assessment of decreasing of groundwater-table using Geographic Information System (GIS) (Case study: Mashhad Plain Aquifer)

Water resource management, especially in groundwater, is very important in arid and semiarid regions. Natural and anthropogenic phenomena have caused critical conditions and fall in groundwater table within last decades in many places of country such as Khorasan Razavi Province. Therefore for assessment of falling of groundwater table, Mashhad Plain, which is one of the important and largest plain in province, was chosen. To do this research, 70 piezometers well were studied during 2 ten-years periods (1987-97 and 1997-2007). Statistical data were first collected and arranged. Afterwards, isopieses and classification of groundwater level were performed by interpolation method in GIS environment using geology, topography and mountain-plain limit maps. Also water level hydrograph were drawn in Excel software. The result of classification of groundwater level maps indicated that groundwater table decreased about 30 meters in central and western regions of aquifer. The concentration of exploitation wells with high debits in this region, has confirmed former findings according to the classification of exploitation map. According to hydrographs, groundwater table has decreased to 12.1 meters during 20 years, 60 cm water level fall annually. Drought, overexploitation, growth of population, increase in agricultural lands and increasing number of wells are the most important factors in decreasing of groundwater table.